BRITAIN will have to let in around seven million immigrants over the next 50 years to pay for its ageing popu­lation, the official financial forecaster warned yesterday.

Increasing the average retirement age by a year could bring in £13bn (PIC POSED BY MODEL)

The rapidly growing number of pensioners and the fact we live longer will take a toll on an already strained health care system.

And the pressure on public finances will become “unsustainable”, the Office for Budget Responsibility said.

Its report said allowing more than 140,000 immigrants into the UK each year for 50 years – equivalent to seven million – would help increase the overall number of people who are in work and improve public finances.

The alternative would be an extra £19billion in tax rises and spending cuts.

Other recommendations in the annual Sustainability Report include cutting the cost of the state pension and increasing the retirement age again.

The report warns that the burden of pensions and health care could wipe out much of Chancellor George Osborne’s spending cuts, leaving the UK with a £65billion hole in its finances.

Stephen Lowe, of Just Retirement, said: “This report makes it clear that the difficulties we already face with an ageing population are going to be far more severe for our children and their children.”

But Sir Andrew Green, of MigrationWatch, described the idea of funding pensioners by encouraging immig­ration as “crazy”. He said: “We are already the most overcrowded country in Europe.

David Cameron has pledged to reduce the flow of immigrants into the country

We need to find a way of managing our economy which does not require millions more immigrants

Sir Andrew Green, MigrationWatch

“We need to find a way of managing our economy which does not require millions more immigrants – who will themselves, get older and require public services.”

And Baroness Sally Greengross, UK chief executive of the International Longevity Centre said: “Increasing the average retirement age by just one extra year could bring in around £13billion.”

But she warned the new financial projections could turn out to be too cautious unless Britain invests in health care and extends people’s working lives.

The report said Britain’s borrowing would rise to 99 per cent of GDP if there was a steady flow of immigrants. A complete ban would put it up to 174 per cent of GDP.